As the technology for nanometer semiconductor fabrications matures, the 0.09 μm process obviously becomes a trend, the nano surface inspection technology will play a decisive role. Basic theories of near-field optics are utilized to obtain an evanescent wave, when the distance between a probe and the surface of a testing object is controlled below the wavelength of light. The near-field evanescent wave can keep the optics measurement resolution from extreme light diffractions to achieve the nano resolution scale. The design theory is to use a point light source having a size smaller than its wavelength to observe the surface of a matter. If the mode field diameter at the light source outlet of a point light source is a and the light intensity at the light source outlet position (z=0) is [3,4], then theoreticallyI(r,z=0)=exp (−r2/a2)  (1)
Equation (1) is transformed by Fourier transforms to obtain a Gaussian distributed transversal wave vector (kr). According to the Fourier optics, it is necessary to detect a transversal wave vector larger than 1/a as to obtain the optical resolution a. Since the vacuum wave vector (k=2π/λ) has the following relation with kr and the wave component vector (kz) in the propagation direction:k2=kr2+kz2
And the high-resolution wave vector (kr) is much larger than the wave vector of vacuum,kz2≈−kr2=>kz≈ikr>i/a  (2)
Therefore, the super resolution cannot be propagated under a helpful mode, and its existing length is smaller than the range of a. If the distance between the point light source and the surface of the testing object is controlled within a range smaller than a, then the evanescent wave will have an effect on several nanometers of the surface of the testing object to provide a super optical resolution. If the surface of the testing object is scanned simultaneously, a high-resolution near-field optical image can be obtained. The lithography technology established by this foundation is known as the near-field optical lithography.
To produce the effect of a near-field optics, it is necessary to keep the distance between an optical fiber probe and the surface of a testing object smaller than the wavelength of the testing light as to break through the resolution for the limit λ/2 of the far-field optics and obtain a super measuring resolution. However, it is uneasy to measure an extremely small distance because the signal produced under such conditions is very weak. Firstly, a wave filter is needed, and then the weak signal is amplified by an amplify circuit for an optoelectronic conversion. Such amplified signal can provide a value approaching to the actual one. Furthermore, it requires a high-precision displacement system for the control, and a precise feedback signal definitely can provide the desired effect.
However, the prior-art displacement system is an XY platform, which only uses a motor or a roller wheel to control the displacement along the X-axis and the Y-axis. Although such arrangement can achieve the effect for the displacement of the XY platform, the precision is not high enough. Another traditional XY platform uses a magnetic levitation technology to control the displacement along the X-axis and Y-axis. Although this kind of XY platform has a high precision, its design is complicated and its cost is very high and not cost-effective.
In view of the shortcomings of the traditional XY platforms, the inventor of the present invention based on years of experience of related field to conduct research and development to overcome the shortcomings and finally invented an XY platform device with nanoscale precision that uses the movements of an optical pickup head in focusing and radial directions to drive the displacement of the XY platform device in order to achieve the high-precision and low-cost effects.